The simultaneous measurement of electric potentials from within the ventricular chambers has become feasible with the development of a rigid multi-electrode intracavitary probe. The objective of this research proposal is to 1) develop quantitative criteria based on intracavitary potential recordings that could be used in electrophysiological studies to determine the extent and location of myocardial infarction and 2) compute and determine the physiologic relevance of computed endocardial potential distributions from measured intracavitary potentials. The objectives of this study would be accomplished using canines with experimentally induced myocardial infarction, providing the ability to test electrocaardiographic variables under experimental conditions most typical of clinical cardiovascular disease. During each canine study, intracavitary potentials would be recorded simultaneously before and after myocardial infarction is produced. Intracavitary potentials would be obtained from a cylindrical probe, 45x10mm in size, introduced into the left ventricle through the left atrium. The probe has 40 evenly spaced recording electrodes on its surface. Electrocardiographic measures to be examined include QRST areas, maximum potential, maximum dV/dt, and intracavitary activation sequences. In addition, the measured intracavitary potentials are defined in terms of mathematically equivalent cardiac generators through multipole analysis. The results would then be correlated with the known state of the myocardium, including infarct size and location, to assess the value of intracavitary recordings in cardiac studies. In the second phase of this investigation, endocardial potentials would be computed from measured intracavitary potentials by an inverse solution. Accuracy would be tested by 1) comparing computed endocardial potentials directly to measured endocardial potentials obtained from plunge needle electrodes and 2) direct comparison of the sequential excitation and repolarization sequences derived from both the measured and computed endocardial potential. The applicant hypothesizes, that intracavitary recordings may be more sensitive to the state of the myocardium and may provide measures with better correlations to physiologic events than epicardial or body surface recordings.